I'm on El Capitan 10.11.6. I upgraded to 4.0.2 today and things just ground to a halt. Youtube videos were slow, if they played at all. Couldn't stream music. SSH connections took ages. I restarted my computer, router, modem, etc but it never got better.
Activity Monitor showed higher usage from Little Snitch that what I think is normal. It also seemed like two copies of it were running at times.
I tried disabling network filtering but things didn't improve. I checked other devices on my wifi network and they were fine. I finally uninstalled and things are back to normal. Anyone else experiencing issues like this?